Since the early days of enantioselective Robinson annulations facilitated by proline, organocatalysis has garnered the attention of the synthetic community. Organocatalysis typically employs mild conditions, are relatively easy to execute, and can be used for a wide variety of chemical transformations. Much of the key reactivity in organocatalysis concerns activating carbonyl moieties via formation of a chiral iminium ion, which resembles nature's method for forming alkaloid natural products. Despite this similarity, relatively little attention has been focused on the application of organocatalysis to alkaloid synthesis. Furthermore, while an intramolecular conjugate addition is often a key ring forming strategy in the synthesis of polycyclic natural products, only limited examples of organocatalyzed, intramolecular Michael addition have been reported.
Certain proline sulfonamides are known. For example, the following proline sulfonamides have been disclosed in the literature.